Slide fastener with woven fabric support and process for making same

ABSTRACT

A thermoplastic monofilament is progressively payed out from a supply reel or extrusion nozzle in step with the advance of a set of warp threads through a shuttleless loom and is periodically inserted into the wrap-thread shed from one side, with the aid of a pusher or a weft needle, in a succession of loops perpendicular to the plane of the warp or inclined with reference thereto. In the first instance each loop defines a pair of aligned shanks of a single turn of a continuous coupling element, whereas in the second instance it forms two mutually offset shanks of a pair of adjoining turns.

United States Patent m1 Fr'dhlich SLIDE FASTENER WITH WOVEN FABRIC SUPPORT AND PROCESS FOR MAKING SAME [75] Inventor: Alfons Friihlich. Essen. Germany [73] Assignee: Opti-Holding AG. Glarus.

Switzerland [22] Filed: Apr. 23, I973 [21] Appl. No: 353,731

[30] Foreign Application Priority Data Apr. 22. I972 Germany .4 22l9907 [52) U.S. Cl. [39/384 B: 24/205: 24/16 C. 139/116 [5| 1 Int. Cl 003d 3/00 [58] Field olSearch 139/11. H6. 118, 124R.

l39/l24 A. 384 B; 24/2U5.l C. 205.!3 C, 205.!3 D. 205.16 R. 205.16 C

[56] References Cited UNITED STATES PATENTS l.fi43 2ll 9/[927 Hulmc 139/] I6 PM Apr. 29, 1975 3.266JI4 8/1966 Gcrlzlck et all. l39/3R4 3.692.068 9/1972 Aver l39/l [6 Primary EmminerHenry S. Jaudon Attorney. Agent. or Firm-Karl F. Ross; Herbert Dubno [57] ABSTRACT A thermoplastic monofilament is progressively payed out from a supply reel or extrusion nozzle in step with the advance of a set of warp threads through a shuttleless loom and is periodically inserted into the wrapthread shed from one side. with the aid of a pusher or a weft needle, in a succession of loops perpendicular to the plane of the warp or inclined with reference thereto. In the first instance each loop defines a pair of aligned shanks of a single turn of a continuous coupling element whereas in the second instance it forms two mutually offset shanks of a pair of adjoining turns.

9 Claims, 18 Drawing Figures :"ATENTEE APR 2 9 i975 SHEET 10F 5 PmEmEnmzsms 3.880.203

SHEET '4 BF 5 FIG/8 PHEHTEB APR 2 9 K95 SHEET 5 BF 5 SLIDE FASTENER WITH WOVEN FABRIC SUPPORT AND PROCESS FOR MAKING SAME FIELD OF THE INVENTION My present invention relates to a stringer to be cut into sections designed to form slide-fastener halves of the type wherein a thermoplastic monofilament. c.g. of nylon or polyester. forms a continuous coupling ele ment with a multiplicity of parallel turns having bight portions provided with coupling heads designed to interlock with similar formations on confronting bight portions of a mating fastener half.

BACKGROUND OF THE INVENTION Coupling elements of this description are generally supported on stringer tapes which may be of substan tially the same width as the element (except for the lat erally projecting coupling heads) or could be somewhat wider. Such supporting tapes can be either knitted or woven.

The conventional technique is to fasten the preformed monofilament to its supporting tape by stitching. this requiring a separate operation. In the case of warp-knit tapes it is possible. as disclosed in my copending application Ser. No. 349.005 filed 9 Apr.

1973. to tie the monofilament into the fabric structure by knitting stitches. With woven tapes. however. the direct interlinking of the monofilament with the basic threads (specifically the warp threads) of the fabric is difficult. Attempts to do so by loading a shuttle with the monofilament for passage through the sheds of the warp threads have met with only limited success. particularly in view of the fact that only relatively short lengths of the comparatively heavy monofilament can be stored on a supply coil in the shuttle.

OBJECTS OF THE INVENTION It is. therefore, an important object of my present invention to provide a stringer adapted to be continuously manufactured by organically incorporating a monofilament of indefinite length. e.g. as issuing from an estruder nozzle. in a fabric structure produced by weaving. preferably with the aid of a shuttleless loom.

A related object is to provide a stringer including a coupling element whose turns are interwoven with the warp threads of a supporting fabric.

SUMMARY OF THE INVENTION The aforestated objects can be realized by advancing a monofilament alongside the path of a set of warp threads in a loom in which two or possibly more groups of these warp threads are relatively displaced. with the aid of heddles. to form alternating sheds as is usual in tape weaving; during each shedding cycle. doubled portions of the monofilament are inserted from one side into some or all of the sheds so as to form elongate loops therein which are interwoven with the warp threads in the continuing weaving process. Thus. the warp threads form pockets in which the loops are firmly held between crossover points.

The technique just described is applicable to a monofilamentary coupling element of the type wherein each one of a multiplicity of such elongate loops. form ing part of that element. comprises a pair of substantially parallel shanks that are interconnected by a front bight portion. each of these shanks being further connected via a respective rear bight portion with a shank of an adjoining turn. The front bight portions. or at least some of them. carry the coupling heads and lie in the plane of the two shanks. this plane being preferably perpendicular to the general direction of the warp threads interlinked therewithv The rear bight portions. extending from one turn to the next. are angularly off set from the front bight portions and lie either at right angles or at an acute angle to the planes of the turns. In the first case the monofilament has a meandering configuration. whereas in the second case it may be regarded as a deformed helix and can thus be described as generally helicoidal. In either case the two shanks of each turn lie at different levels. with reference to the warp plane. and will be referred to hereinafter for convenience as lower" and "upper shanks even though their relative geometrical orientation is immaterial and subject to change.

During the weaving process. in accordance with my present invention. the monoflament extends along the front edge of the evolving coupling clement. i.e. on the side of the coupling heads. In a known process (see US. Pat. No. 3.662.068). in which the undeformed monofilament is fed in from the rear edge. the loops so formed extend toward the front or working edge and correspond to the turns of the coupling element. i.e. each loop comprises the upper and the lower shank of a turn as well as the front bight portion interconnecting same. Upon insertion of the monofilament from the front edge. each of the rearwardly extending loops comprises the upper shank of one turn and the lower shank of an adjoining turn together with their connecting rear bight portion. It is also possible to start from an intermediate location. between two groups of warp threads to be interwoven with different parts of the monofilament.

The pockets containing the monofilament loops could also be occupied by weft threads (or sections of a continuous weft thread) introduced by a conventional weft-insertion needle and tied into a selvedge on the edge opposite the insertion side. In many instances. however. especially where the width of the tape is less than that of the monofilamentary coupling element. no weft is needed since the warp threads are held together by the loops of that element interwoven therewith.

BRIEF DESCRIPTION OF THE DRAWING The above and other features of my invention will now be described in detail with reference to the accompanying drawing in which:

FIG. I is a plan view of a representative portion of a pair of interlinked slide-fastener halves derived from stringers embodying the invention:

FIGS. 2., 3 and 4 are sectional views respectively taken on lines II II. III III and IV IV of FIG. 1;

FIG. 5 is a plan view similar to FIG. 1. showing a representative portion of a modified slide-fastener half or stringer according to my invention.

FIGS. 6. 7 and 8 are sectional views respectively taken on lines VI VI. VII VII and VIII VIII of FIG. 5;

FIG. 9 is a plan view similar to FIG. 5. illustrating a conventional slide-fastener half for the sake of comparison;

FIGS. I0 and II are sectional views respectively taken on lines X X and XI XI of FIG. 9;

FIG. 12 is another plan view similar to FIG. 5. showing a modification of the stringer of FIGS. 9 II in accordance with my invention;

FIGS. [3 and 14 are sectional views respectively taken on lines Xlll XIII and XI\' XI\' of FIG. 12;

FIG. I is a perspective view of part of an insertion mechanism included in a tape loom for making a stringer in accordance with my imention;

FIG. 16 is an elevational view taken on line XVI XVI of FIG. I5;

FIG. 17 is a perspective detail view of a modified in sertion mechanism. and

FIG. 18 is a highly schematic perspective view. illustrating a further modification.

SPECIFIC DESCRIPTION Reference will first be made to FIGS. l5 and 16 in which I have illustrated certain elements ofan insertion mechanism included in a tape loop whose conventional parts. designed to guide two groups of warp threads l3. [3" along a predetermined path for weaving a nar row fabric. have not been shown. The loom operates without a shuttle. yet for producing the patterns of FIGS. 9 14 it is equipped with the usual weftinsertion and selvedging needles.

A thermoplastic monofilament I is continuously sup plied from a nonillustrated source which could be a large reel or an extrusion nozzle. This filament passes through an eye of a swingable guide arm 21 into the path of a reciprocable plunger 22 which confronts a fork 23 having two symmetrical prongs 23'. 23" (the latter being shown partly broken away in FIG. Prongs 23'. 23" have curved cheeks 25'. 25" forming a passage 26 for plunger 22 whose front end has a vertical depression 22' engageable with a vertical stretch of filament l which at this instant crosses the passage 26 from above. having beenbent about a forward extension of check 25' by a preceding downward swing of guide arm 2|. The forward thrust of plunger 22 through passage 26 doubles the confronting monofilament portion into a vertical loop with an upper horizontal shank 3 and a lower horizontal shank 4 interconnected by a front bight portion 5. Shank 3 comes to lie in a peripheral notch 27' of an upper transport wheel 28' whereas shank 4 is received in a similar notch 27" of a lower transport wheel 28". The two wheels 28' and 28" are rotated clockwise and counterclockwise. respectively. as viewed in FIG. 16. by one notch upon every withdrawal of plunger 22 into the position shown in FIG. IS. This rotation lets the filament I pass horizontally between alternate notch pairs 27', 27" to form upper and lower rear bight portion 14 and 11. respectively. Guide arm 2l swings down after the formation of each upper bight portion 14 and swings up after the formation of each lower bight portion I]. with the filament I bending alternately about the upper and the lower edge of check 25'.

A heated plate 29, fixedly positioned in line with plunger 22. men es to flatten a part of bight portion 5 into a coupling head 6 at the end ofthe insertion stroke of the plunger indicated by an arrow [8. This is made possible by the fact that the plunger 22 inserts the filament 1 into the warp pockets from the rear edge ofthe fabric. ie the edge remote from the working edge of the fastener element defined by the coupling heads 6. If that insertion stroke 18 proceeds in the opposite direction. eg as needed to form the pattern of FIGS. 12

- [4 described hereinafter. separate means (as shown. for example. in commonly owned US. Pat. No. 3.665.56I may be provided to form these heads.

The motion of the heddles [not shown) carrying the warp threads l3. 13" is. of course. synchronized with that of plunger 22, arm 21 and wheels 28. 28" to reverse the shed after the completion of each loop 3 6.

In FIG. 17 l have illustrated part ofa modified insertion mechanism in which the plunger 22 has been replaced by a needle 32 having an eye 32 for the passage of the filament I. At the end of each insertion stroke. a detent arm 34 is introduced into the loop just formed to engage its bight portion 5., projecting beyond the warp threads. during withdrawal of needle 32 and until the reversal of the shed. A heated block 33 can be advanced. following such withdrawal. toward the detent arm to form a coupling head. If the coupling element is to be of meandering shape, arm 34 may be alternately raised and lowered so as to engage the needle from above and from below to let it return to its withdrawn position either along the lower shank 4 or along the upper shank 3 of the loop just formed. Needle 32, besides being sufficiently flexible for such alternate engagement. is also rotatable about its axis through twice to minimize friction during formation of the front and rear bight portions. (With a helicoidal coupling element. as shown in FIGS. 9 [4, the angular offset of the two bight portions is different from 90.) The forced rotation of the needle. under the control of the same nonillustrated programmer that times its linear reciprocation and the correlated motions of the other elements of the loom. eliminates the need for a swingable arm 21 as shown in FIG. 15. At the opposite end. loop 3 5 is restrained by the warp threads intersecting in the region of the rear bight portions; if desired. however. a second detent arm similar to arm 34 could be provided at the rear edge of the fabric to engage these bight portions during the insertion strokes of the needie.

If the filament l is still in a heat-softened state on reaching the insertion mechanism. loop formation will be facilitated; in that case it may even be possible to dispense with the heating of the head-forming means 29, 33. Alternatively. the filament may be reheated (e.g. by infrared radiation) along sections subject to deformation by plunger 22 or needle 32.

Different types of weave patters embodying my invention will now be described with reference to FIGS. 1 14 where the various loop sections of monofilament l are identified by the same reference numerals as above.

In FIGS. 1 4 the filament l is given a meandering shape. with turns 2 lying in planes perpendicular to the general direction of warp threads l3. l3. 13" here assumed to be horizontal. Each turn 2 consists of an upper shank 3. a front bight portion 5 with coupling head 6. and a lower shank 4; also formed are elongate loops which consist of rear bight portions 14 and I] respectively interconnecting the upper shanks 3 and the lower shanks 4 of adjoining turns 2. these two groups of bight portions thus lying at different levels as also seen in FIGS. l5 and 16.

The two slide-fastener halves shown in FIGS. l and 2 are identical and produced in identical manner. A small number of warps l3. l3" embraces pairs of adjoining turns 2 of the corresponding coupling element 1. as best seen in FIG. 4; these warps have been drawn in heavier lines. for emphasis. even though they need not actually be heavier than the more numerous warp threads 13 shown in thin lines. The latter warp threads are divided into two parallel subsets 13a. [3h at the levels of shanks 3 and 4. respectively; these groups are individually shedded. in mutually staggered relationship. as best seen in FIG. 3.

In the continuous production of a stringer from which the interlocking fastener hal\cs of FIGS. I 4 can be cut. a mechanism somewhat more complex than that of FIGS. 15 and 16 may be used. as schematically illustrated in FIG. 18 where the transport wheels 28'. 28" and other guide means have been omitted for clarity's sake with the exception of a fixed plate 35 whose front surface lies in a vertical plane between warps 13 (not shown in FIG. [8) and 13'. I3". i.e. the plane corresponding to section line I" III. IV IV of FIG. I. The monofilament l arrives in the same plane. being alternately supplied from above and from below as in the system of FIGS. IS and 16. The insertion mechanism of FIG. 18 includes three plungers 22a. 22b. 22c operating at different levels Plunger 22a moves at the level of upper shanks 3 and. in its rearwardly directed insertion stroke (arrow 18a). passes through the shed of warp threads 1311. FIG. 3. to form an upper rear bight portion [4 linking two adjoining turns 2. The lower rear bight portions I] are formed by the plunger 22h whose insertion stroke is also rearwardly directed (arrow 18b) and which moves at the level of lower shanks 4. passing through the shed of warp threads 13!). Plunger 22('. moving at an intermediate level between the two groups of warp threads I341. I3!) so as not to interfere with their shedding. spans two turns 2 of the meandering filament l and is forwardly displaceable from a retracted position. in line with the plate 35. to an advanced position to form a pair of adjoining front bight portions 5; this movement may be accompanied by the formation of coupling heads 6 with the aid of an advantageously heated counterplate as shown at 29 in FIG. 15.

After the advance of plunger 22c into its illustrated working position. and upon the subsequent retraction of plungers 22a and 22h. warps 13'. 13" are reversed. Plunger 221: then inserts an upper loop. consisting of two adjoining shanks 3 and a bight portion I4. into the shed of warp threads I3u. Thereafter. plunger 22b operates to insert a lower loop. consisting of two adjoining shanks 4 and a bight portion 11. into the shed of warp threads 13h. Next. all three plungers are withdrawn whereupon the fabric advances by two turn spacings to bring the newly formed meander sections into line with plunger 22(' which then again advances to complete the formation of two further front bight portions 5. The cycle is now repeated.

One of the upper loops, inserted by plunger 2211. and one of the lower loops. inserted by plunger 2211. have been particularly indicated in FIGS. I and 3 by distinctive shading. The loop-receiving pockets formed by warps I3. 13' have been designated [2; those formed by warps 13a. 13!: have been indicated at I211, I212.

The separation of the upper and lower warp subsets 13a. 13b facilitates the use of a flat slider 36 with two wings received between shanks 3 and 4 on opposite sides of the two rows of coupling heads 6 flanked by warps l3. 13''. as illustrated in phantom lines in FIG. 2. Such a slider has been disclosed in my copending ap plication Ser. No. 348.1 10 filed 5 April 1973.

In FIGS. 5 8 I have shown a stringer similar to that from which the slide-fastener halves of FIGS. 1 4 are cut. except that working turns consisting of upper shanks 3. lower shanks 4 and front bight portions 5. carrying coupling heads 6 alternate with shorter dummy turns consisting of upper shanks 9. lower shanks I0 and front bight portions 15. Bight portions I5 terminate ahead of the warp threads I3. 13" embracing the projecting front parts of the working turns; this requires a modification of the insertion mechanism of FIG. 18 to limit the width of plunger 22c to one turn while guide plate 35 is extended to engage a third turn. i.e. the second from the left in that Figure. The dummy turns serve as mechanical reinforcements for the working turns by reducing the mutual separation of the shanks of adjoining turns; the foreshortening of the dummy turns provides the necessary space for penetration by the coupling heads of the mating fastener half. Elongate loops are formed by upper shanks 3.9 and bight portions [4 as well as by lower shanks 4.10 and bight portions 11.

In FIGS. 9 II the turns 2 are of the same length. as in FIGS. I 4. but are interconnected by slanting rear bight portions 7 linking the upper shank 3 of one turn with the lower shank 4 of an adjoining turn. Thus. the coupling element now has a generally helicoidal rather than meandering shape. The direction of insertion. as indicated by arrow 18. is from right to left (i.ev toward the working edge defined by coupling heads 6i as described with reference to FIGS. I5 and 16. the sloping of the bight portions 7 being accomplished by suitable correlation of the motions of guide arm 2] and transport wheels 28'. 28". Again. an inserted loop consisting of shanks 3.4 and a bight portion 5 has been indicated by distinct shading in FIGS. 9 and 10.

The shedding ofthe loop-embracing warp threads 13 is synchronized with the motion of a nonillustrated weft-insertion needle carrying a weft thread [9 which not only traverses the pockets [2 formed by the warp threads 13 but also is interwoven. in conventional manner. with supplemental warp threads l3.v in a region adjacent the coupling element 1 to provide a wider stringer tape. The laterally extending part 8 of this stringer tape can be folded under the coupling element I to expose the heads 6 when the fastener half is sewn onto a garment or other article to be equipped therewith.

As illustrated in FIGS. I2 I4. a similar slidefastener half may be produced by the insertion of elongate Ioops 17 in the reverse direction (arrow 18) into the shed of warps I3. each of these loops consisting of an upper shank 3 of one turn 3-5. a lower shank 4 of an adjoining turn 3-5 and a bight portion 7 linking same. Weft thread I9 again passes through pockets l2 and is interwoven not only with supplemental warp threads 13x. forming an extended tape portion 8. but also with additional warp threads 13 interspersed with the main warp 13 but lying below the fastener coil I without engaging its shanks. In this instance. the extended tape portion lies on the side of the coupling element remote from its working edge. One of the loops has again been distinctly shaded. for emphasis. in FIGS. 12 and I4.

I claim:

I. A slide-fastener stringer comprising a continuous monofilamentary coupling element with a multiplicity of parallel turns. each of said turns including a pair of substantially parallel shanks interconnected by a front bight portion coplanar therewith. a shank of each turn being connected with a shank of an adjoining turn by a rear bight portion. at least some of said front bight portions being provided with coupling formations. and a set of generally parallel warp threads extending substantially at right angles to the planes of said turns. said warp threads being interlinked in a weave pattern with elongate loops forming part of said coupling element. said loops being received in respective pockets formed by intersecting warp threads. each of said loops consisting of a pair of shanks of adjoining turns interlinked by a rear bight portion.

2. A slide-fastener stringer as defined in claim I wherein said coupling element is of meandering shape with a first shank of each turn disposed at a first level and a second shank of each turn disposed at a second level. said rear bight portions lying alternately at said first and second levels. said set of warp threads including a first subset at said first level forming pockets around loops which include said first shanks of adjoining turns and a second subset at said second level forming pockets around loops which include said second shanks of adjoining turns.

3. A slide-fastener stringer as defined in claim 2 wherein the shanks of said loops have parts projecting forwardly from said pockets. said set of warp threads further includes a plurality of additional warp threads alongside said subsets forming pockets around the forwardly projecting parts of the shanks ofrespective pairs of adjoining turns.

4. A slide-fastener stringer as defined in claim 3 wherein said turns include longer working turns carrying said coupling formations and shorter dummy turns without coupling formations interleaved with said working turns. said additional warp threads engaging only said working turns along portions thereof projecting beyond said dummy turns.

5. A slide-fastener stringer as defined in claim 1 wherein said coupling element is of generally helicoidal (ill shape. each loop lying in a plane including an acute angle with the planes of said turns.

6. A slide-fastener stringer as defined in claim I. further comprising weft-thread means interwoven with said set of warp threads and extending laterally beyond said coupling element. and supplemental warp threads interwoven with said weft-thread means alongside said coupling element.

7. A slide-fastener stringer as defined in claim 6, further comprising ancillary warp threads interlinked with said weft-thread means in the region of said coupling element but disengaged therefrom.

8. A process for making a slide-fastener stringer. comprising the steps of:

advancing a set of generally parallel warp threads along a predetermined path, said set including a first and a second subset lying at a first and a second level. respectively;

relatively displacing groups of said warp threads within each subset to form alternating sheds there between;

advancing a thermoplastic monofilament alongside said warp threads. and

inserting doubled portions of said monofilament from one side. alternately at said first and second levels. into respective sheds of said first and second subsets to form loops interwoven with said warp threads. each loop including two parallel shanks disposed at the same level. the shanks at said first level forming turns of a coupling element with juxtaposed shanks at said second level linked therewith via respective bight portions.

9. A process as defined in claim 8. comprising the fa rther step of interweaving additional warp threads of said set with parts of said shanks projecting beyond said first and second subsets in the vicinity of said bight portions. said additional warp threads being formed into sheds around the projecting parts of respective pairs of adjoining turns. 

1. A slide-fastener stringer comprising a continuous monofilamentary coupling element with a multiplicity of parallel turns, each of said turns including a pair of substantially parallel shanks interconnected by a front bight portion coplanar therewith, a shank of each turn being connected with a shank of an adjoining turn by a rear bight portion, at least some of said front bight portions being provided with coupling formations, and a set of generally parallel warp threads extending substantially at right angles to the planes of said turns, said warp threads being interlinked in a weave pattern with elongate loops forming part of said coupling element, said loops being received in respective pockets formed by intersecting warp threads, each of said loops consisting of a pair of shanks of adjoining turns interlinked by a rear bight portion.
 2. A slide-fastener stringer as defined in claim 1 wherein said coupling element is of meandering shape with a first shank of each turn disposed at a first level and a second shank of each turn disposed at a second level, said rear bight portions lying alternately at said first and second levels, said set of warp threads including a first subset at said first level forming pockets around loops which include said first shanks of adjoining turns and a second subset at said second level forming pockets around loops which include said second shanks of adjoining turns.
 3. A slide-fastener stringer as defined in claim 2 wherein the shanks of said loops have parts projecting forwardly from said pockets, said set of warp threads further includes a plurality of additional warp threads alongside said subsets forming pockets around the forwardly projecting parts of the shanks of respective pairs of adjoining turns.
 4. A slide-fastener stringer as defined in claim 3 wherein said turns include longer working turns carrying said coupling formations and shorter dummy turns without coupling formations interleaved with said working turns, said additional warp threads engaging only said working turns along portions thereof projecting beyond said dummy turns.
 5. A slide-fastener stringer as defined in claim 1 wherein said coupling element is of generally helicoidal shape, each loop lying in a plane including an acute angle with tHe planes of said turns.
 6. A slide-fastener stringer as defined in claim 1, further comprising weft-thread means interwoven with said set of warp threads and extending laterally beyond said coupling element, and supplemental warp threads interwoven with said weft-thread means alongside said coupling element.
 7. A slide-fastener stringer as defined in claim 6, further comprising ancillary warp threads interlinked with said weft-thread means in the region of said coupling element but disengaged therefrom.
 8. A process for making a slide-fastener stringer, comprising the steps of: advancing a set of generally parallel warp threads along a predetermined path, said set including a first and a second subset lying at a first and a second level, respectively; relatively displacing groups of said warp threads within each subset to form alternating sheds therebetween; advancing a thermoplastic monofilament alongside said warp threads; and inserting doubled portions of said monofilament from one side, alternately at said first and second levels, into respective sheds of said first and second subsets to form loops interwoven with said warp threads, each loop including two parallel shanks disposed at the same level, the shanks at said first level forming turns of a coupling element with juxtaposed shanks at said second level linked therewith via respective bight portions.
 9. A process as defined in claim 8, comprising the further step of interweaving additional warp threads of said set with parts of said shanks projecting beyond said first and second subsets in the vicinity of said bight portions, said additional warp threads being formed into sheds around the projecting parts of respective pairs of adjoining turns. 